Flexible stent

ABSTRACT

A flexible tubular stent including loosely interlocked annular elements without intersections or cross-over points.

BACKGROUND OF THE INVENTION

[0001] This invention relates to stents which are implanted in the body.

[0002] Stents are used in body lumens, such as blood vessels to maintainthem in an open condition. Typically, the stent is delivered into thelumen by a catheter that supports the stent in a compact form duringpercutaneous insertion and transport through a lumen, such as a vessel,to the desired implantation site. Upon reaching the site the stent isexpanded so that it engages the interior wall of the vessel. Thecatheter is then removed, leaving the stent in the body.

[0003] The expansion of the stent may involve forcing it to expandradially outwardly as by inflation of a balloon carried by the catheteror the stent may be of a self-expanding type, several of which are knownin the art. For example, the stent may be made of a memory metal such asNITINOL which self-expands in selected temperature ranges.

[0004] It can be readily seen that the more flexible the stent is duringpercutaneous insertion the more easily it can negotiate bends and curvesin the lumen or vessel to reach the implantation site.

SUMMARY OF THE INVENTION

[0005] This invention provides a stent design of individual annularelements shaped so as to loosely interfit or interlock together withoutintersection or cross-over points whereby the stent exhibits unusualflexibility.

[0006] Preferably, the annular elements are multiple independentserpentine-like rings adjacent to each other having laterally spaceddouble segments 180° out of phase with each other to provide a steppedsequence around each ring, each segment having a wide and a narrowintermediate portion with one set of segments on one side being fittedinto an adjacent set of segments on one side of an adjacent serpentinering to interlock the rings together against longitudinal separationthus forming a flexible cylindrical or tubular structure.

[0007] In another aspect of the invention, the edges of the annularrings may be formed at an angle with respect to the center line of thetubular stent configuration rather than aligned therewith as in theprior art. By fabricating the stent with such angular side walls “offcenter” the rings will interlock with one another against radialseparation if moved radially in or out with respect to the stentcenterline.

BRIEF DESCRIPTION OF THE DRAWING

[0008]FIG. 1 is a side view of a stent according to a preferred form ofthe invention;

[0009]FIG. 2 is an enlarged portion of FIG. 1 showing in detail theloosely interlocked serpentine rings;

[0010]FIG. 3 is an enlarged fragmentary showing of a form of theinvention having segments with angular side walls;

[0011]FIGS. 4 and 5 are end view of a stent showing their cylindricalconstruction and the unique cross-sectional shapes of the struts;

[0012]FIG. 6 shows overlap in stent struts, and

[0013]FIGS. 7 and 8 are enlarged portions of stents according to thisinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Referring to FIGS. 1 and 2, an embodiment of a stent according tothe invention is shown and generally designated at 10. Stent 10 is ofcylindrical or tubular configuration as can be seen in end view FIGS. 4and 5 and includes a plurality of annular serpentine segments 12 spacedadjacent to each other and interfitted with each other over the lengthof the stent body.

[0015] Each annular segment 12 is of a generally serpentineconfiguration having wide lateral end portions 14 and narrow lateralportions 16 spaced from ends 14, the wide portions of one ring beinginterfitted into the wide portion of an adjacent ring as shown toprevent longitudinal separation of the serpentine rings. Radialseparation of the rings is prevented during handling and delivery bycarrying the interfitted rings on a shaft (not shown) as may be providedby the delivery catheter per se.

[0016] The stents of the invention may be made of wire or the like. Morepreferably, they are laser cut from a metal cylinder to a desiredconfiguration.

[0017] Historically stents have been constructed of struts with eitherround, square, trapezoidal, oblong, or other cross-sections. Thecross-section of the strut has remained relatively constant throughoutthe stent. The shape of the strut has been dictated by the startingmaterial, the cutting or shaping process, and the surface finishprocess. Stent designers can select from a variety of shapes to give thestent unique mechanical properties, but the stent contains the samegeneral cross-section throughout, i.e., if the strut is oblong in shapeit remains oblong, if the strut is wider on the OD than the ID itretains this profile throughout the stent. This remains true even if thecross-sectional area of the strut varies in regions of the stent.

[0018] A further improvement is shown in FIGS. 3, 4 and 5 in whichsegments 18 may be formed from a tube or sheet have the side walls “offcenter” with respect to the center line of the stent so that thesegments interlock with one another if moved radially in or out. Twooptions are shown. FIG. 4 shows the struts laser cut off axis of thecenter of the stent all in the same direction. FIG. 5 shows a secondoption in which the off-axis direction of cut alternates around thestent.

[0019] The result is a stent which contains multiple varied strutcross-sectional shapes. This attribute is desirable because eachcross-sectional shape is selected to give the stent unique mechanicalproperties at that specific location within the stent. By either using ameans to selectively remove material or mechanically deform thematerial, the stent struts can be formed into a tailored shape atselected locations. These tailored shapes can cause the struts to bestronger, weaker, remain flat during expansion, twist during expansion,etc.

[0020] Also, varying the cross-section of the stent struts can improvethe nesting or the compaction of the struts in the compressed state. Byimproving the compaction properties of the stent, the stent can achievelower profiles. There can even be overlapping regions of the variousstruts without actually causing struts to be deformed into the ID or ODof the stent. This helps to maintain a low profile. Additionally, theoverlapping of the struts creates a securement means. Each row of strutswill help to contain an adjacent row. This is shown in FIG. 6.

[0021] Referring now to FIG. 7, there is shown an example of a stent 10in fragment to illustrate that a stent according to the invention may bemade of a single elongated piece of wire or the like.

[0022] In FIG. 8, interconnections 20 are shown between rings 12 in astent 10, showing in plan.

[0023] The above Examples and disclosure are intended to be illustrativeand not exhaustive. These examples and description will suggest manyvariations and alternatives to one of ordinary skill in this art. Allthese alternatives and variations are intended to be included within thescope of the attached claims. Those familiar with the art may recognizeother equivalents to the specific embodiments described herein whichequivalents are also intended to be encompassed by the claims attachedhereto.

What is claimed is:
 1. A flexible expandable stent comprised of aplurality of serpentine-like rings loosely interfitted in matedrelationship with adjacent serpentine rings to form a mesh-likecylindrical stent body.
 2. The stent of claim 1 wherein each ring iscomprised of a plurality of segments, each having alternating wide andnarrow portions to facilitate interfitting thereof.
 3. The stent ofclaim 1 in which the rings are unconnected with each other.
 4. The stentof claim 1 in which the rings are interconnected to each other.
 5. Thestent of claim 1 in which the serpentine rings are formed of wire. 6.The stent of claim 5 in which the wire is a continuous length of wireextending through the entire stent body.
 7. The stent of claim 1 inwhich the serpentine rings are formed of material having substantiallyflat sides.
 8. The stent of claim 1 in which the rings are cut from ametal tube whereby a plurality of substantially flat sided struts incross-section are provided.
 9. The stent of claim 8 in which edges of atleast some of the struts are angled with respect to the edges ofadjacent struts whereby radial separation is prevented.
 10. The stent ofclaim 1 in which the cross-section of the rings are varied in apredetermined manner to provide selected properties to various portionsof the stent.
 11. A stent comprised of structural elements in which atleast some of the elements have certain predetermined cross-sectionalconfigurations.
 12. The stent of claim 11 in which the cross-sectionalshapes of the elements vary at different locations of the stent.